What is a skully cap

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I was riding the train yesterday crocheting, and a young man sat beside me started telling me how his grandma crochet etc. He ask someone to make a skully hat awhile back and she did not know what he was talking about. He describe it as a hat without the rim with elastic around the end. He said he use to live in NY, and they were quite popular awhile back. He said he went back to NY last year and could not find any. He said in the South they call them something starting with T not quite sure. I think it's a beanie hat, anyone knows what he is talking about.